This invention relates to a scanning apparatus configured to transmit scanning pulses at a sample and receive reflections of those pulses from the sample.
Ultrasound is an oscillating sound pressure wave that can be used to detect objects and measure distances. A transmitted sound wave is reflected and refracted as it encounters materials with different acoustic impedance properties. If these reflections and refractions are detected and analysed, the resulting data can be used to generate images of the environment through which the sound wave traveled.
Ultrasound can also be used to scan a physical object. Most ultrasound frequencies are attenuated strongly by air and air-object boundaries tend to show a big impedance mismatch. Some form of coupling medium is needed if the ultrasound signals are to penetrate the object sufficiently. Often the coupling medium is a liquid, such as water or some form of gel.
Ultrasound can be used to identify particular structural features in an object. For example, ultrasound may be used for non-destructive testing by detecting the size and position of flaws in a sample. Non-destructive testing is typically performed in an industrial environment in which it is not practical to use a liquid coupling medium. U.S. Pat. No. 5,773,811 describes scanner that can be used for identifying material flaws in the course of non-destructive inspection procedures. It uses a gel pack to couple ultrasound energy into the substrate. This is more practical than using an uncontained gel but it can be difficult to accurately determine the depth of features below the substrate's surface. Dry couplings are also available, such as in the matrix code reading system of U.S. Pat. No. 8,453,928. Sample surfaces tend to be fairly flat in matrix-code reading applications, however, whereas surfaces are often uneven in non-destructive testing applications. Non-destructive testing applications also require the scanner to scan to greater depths than matrix-code reading applications.